The addition or removal of phosphate groups to or from target proteins are two of the most important signaling events in the cell and, as a result, regulate many diverse cellular processes. Thus, methods that detect the addition of a phosphate group (i.e., phosphorylation) or the removal of a phosphate group (i.e., dephosphorylation) of a target protein are highly useful. Phosphate groups are also transferred in other reactions of biological importance.